Can an opponent always kill Zhonya with Salvage before combat starts, preventing it from saving a unit that would die in combat?

Ruling: Yes, if Zhonya is face-up in play, the opponent can wait until they have Focus and use Salvage to destroy it before combat begins. If Zhonya is Hidden, you can play it at Reaction speed during a chain or after your opponent has played their last card or is out of resources, but if you play it just to get it in play, the opponent can Salvage it the next time they have Focus.

Sequence:

• If Zhonya is face-up, opponent can destroy it with Salvage when they have Focus before combat
• If Zhonya is Hidden, you can play it at Reaction speed during a chain to immediately save something
• If you play Hidden Zhonya just to get it in play (not reactively), opponent can Salvage it next time they have Focus

Nuances:

• You cannot react to combat itself, only to spells on the chain
• Playing Hidden Zhonya at Reaction speed during a chain can immediately save a unit before opponent can respond
• If opponent is holding up 2 energy and knows you have Zhonya, they can wait to Salvage it